A conventional upright vacuum cleaner includes a floor engaging main body or foot having a nozzle formed with a nozzle opening. An agitator is typically rotatably mounted within the nozzle, and a dirt duct is formed in the main body and communicates at one end with the nozzle and at an opposite end with vacuum-generating means, such as a motor-fan assembly. The motor-fan assembly typically communicates with a duct to draw a flow of dirt-laden working air through the main body and into a dirt collecting filter bag, which removes the dirt and allows substantially clean air to be returned to the environment through the walls of the filter bag.
The motor fan assembly typically includes a motor housing that encloses a motor. The motor rotatably drives a shaft to which a working fan is suitably coupled such that the working fan rotates with the shaft. As the motor rotates with the motor housing, heat is generated within the motor. To prevent overheating of the motor, a cooling fan is typically provided. In one example, the cooling fan is provided on an end of the shaft opposite the working fan. The cooling fan draws a stream of cooling air into the motor housing through a plurality of cooling air inlets often formed in the motor housing. The cooling air then flows across the motor and is expelled from the motor housing through one or more exhaust openings in the motor housing. The exhaust openings are often located at an end of the motor housing opposite the working air inlet. The cooling air prevents debris and other particles from passing through the motor, for example, when it exits the exhaust openings in the motor housing of a conventional vacuum cleaner. In U.S. Pat. No. 6,880,201, the cooling air can be directed along with the working air in the collection bag so that cooling air is filtered before being exhausted into the atmosphere.
In other vacuum cleaners, the working air is filtered before reaching the motor-fan assembly. Such designs are common in tank-type vacuum cleaners where working air enters a tank inlet, generally through a hose. The tank is under negative pressure through the operation of a motor-fan assembly that draws working air out of the tank. In order to reach the motor-fan assembly, the working air must pass through one or more filtering elements, such as a filter bag or cartridge filter, before passing through the fan and back out into the environment. Such vacuums are often referred to as clean-air designs since the working air has been “cleaned” before reaching the fan. If the bag or cartridge filter is made of HEPA materials, the working air is effectively receiving HEPA filtration before being exhausted to the environment.
Clean air designs may have cooling fans for cooling the motor. Typically, cooling air is drawn through the motor-fan housing through the motor and back out into the environment without filtration. The cooling air can have particulate material in it, for instance, created from the brushes in the motor's commutator, or simply from the environment when drawn into the housing by the cooling fan. Combining the cooling air with the working air adjacent the motor, such as is shown in U.S. Pat. No. 6,880,201, is not a viable solution since the working air in a clean-air design is already cleaned by the time it reaches the motor.